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                小强的书架                </h1>
                <p>时间限制：20s&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;  空间限制：256MB</p>			</div>
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                                <h3>题目描述</h3><p><div>小强有很多书，它想制作一个书架。</div>
<div>对于每本书，它有一个高度、一个厚度。书架的一层能够放置的书的厚度总和不能超过一个</div>
<div>常数W。小强想让每层书架里的书都用一种雅观的方式进行摆放，它经过思考之后认为，</div>
<div>一层书架的高度应该由下式给出：</div>
<div>First+Second+(W-s)/10</div>
<div>其中，First和Second分别是这层书架中高度前两高的书的高度（如果这层只有一本书，</div>
<div>那么令First、Second等于这唯一一本书的高度；如果这层有超过一本高度相同的书都是</div>
<div>最高的，那么First、Second都等于这个最高高度），s表示这层书架的厚度的总和。注</div>
<div>意，每层书架的高度可以不一样。</div>
<div>小强把书从1到N编号，它规定，书架的一层中放置的书的编号必须是连续的。小强想知</div>
<div>道，把所有的书都放进去，它的书架至少要多高呢？</div>
<div></div>
<p></p></p><hr/><h3>输入格式</h3><p><div>第一行两个正整数N和W，表示书的数目和一层书架里的书的厚度总和</div>
<div>的上限。N行，每行两个正整数，按编号顺序依次描述了每本书的高度和厚度。输入数据保证每本书</div>
<div>的厚度都不超过W，高度不超过100000000。</div>
<div></div>
<p></p></p><hr/><h3>输出格式</h3><p><div>一行一个数，精确到小数点后一位，表示书架的最小高度。</div>
<div></div>
<p></p></p><hr/><h3>样例输入</h3><pre>5 10
3 5
7 2
1 3
5 2
6 3</pre><hr/><h3>样例输出</h3><pre>19.5</pre><hr/><h3>提示</h3><p><div>【样例解释】</div>
<div>第一本书自己一层，高度3+3+5/10=6.5，剩下4本书一层，高度7+6+0/10=13。总</div>
<div>共19.5的高度。</div>
<div>【数据规模】</div>
<div>对于100%的测试数据，N&lt;=300000，W&lt;=1000000000</div>
<p></p></p><hr/><h3>题目来源</h3><p>没有写明来源</p>
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